Hard magnetic composition, permanent magnet powder, method for permanent magnet powder, and bonded magnet

ABSTRACT

A single phase consisting of a ThMn 12  phase can be obtained by having the composition thereof represented by a general formula R(Fe 100-y-w Co w Ti y ) x Si z A v  (in the general formula, R is at least one element selected from rare earth elements (here the rare earth elements signify a concept inclusive of Y), Nd accounts for 50 mol % or more of R, and A is N and/or C) in which the molar ratios in the general formula are such that x=10 to 12.5, y=(8.3−1.7×z) to 12.3, z=0.1 to 2.3, v=0.1 to 3 and w=0 to 30, and the relation (Fe+Co+Ti+Si)/R&gt;12 is satisfied.

TECHNICAL FIELD

The present invention relates to a hard magnetic compound suitable as amaterial for permanent magnets used in devices and machines whichrequire magnetic field such as speakers and motors. Additionally, thepresent invention relates to a magnet powder suitable as a material forpermanent magnets, in particular, a material for bonded magnets, and amethod for producing the magnet powder.

BACKGROUND ART

Among rare-earth magnets, an R-T-B system rare earth permanent magnethas been used in various electric appliances such as speakers and motorsbecause magnetic properties thereof is excellent, and a main componentthereof, Nd, is abundant as a natural resource and relativelyinexpensive.

However, in these years, demand for downsizing of electric devices andmachines has grown markedly, and accordingly development of newpermanent magnet materials has been advanced.

Among such materials are rare earth-iron system magnet materials, havinga body-centered tetragonal structure or a ThMn₁₂-type structure,reported in, for example, Japanese Patent Laid-Open Nos. 63-273303,4-241402, 5-65603 and 2000-114017.

Japanese Patent Laid-Open No. 63-273303 discloses a rare earth permanentmagnet represented by a formula, R_(x)Ti_(y)A_(z)Fe_(a)Co_(b) (in thisformula, R is one of the rare earth elements inclusive of Y; A is one ormore of B, C, Al, Si, P, Ga, Ge, Sn, S and N; and x is 12 to 30% byweight, y is 4 to 10% by weight, z is 0.1 to 8% by weight, a is 55 to85% by weight, and b is 34% or less by weight, respectively). JapanesePatent Laid-Open No. 63-273303 describes that the element A intervenesbetween atoms to modify the Fe—Fe distances along preferable directions.

Japanese Patent Laid-Open No. 4-241402 discloses a permanent magnetrepresented by a formula, R_(x)M_(y)A_(z)Fe_(100-x-y-z) (in thisformula, R is at least one element selected from rare earth elementsinclusive of Y; M is at least one element selected from Si, Cr, V, Mo,W, Ti, Zr, Hf and Al; A is at least one element selected from N and C;and x is 4 to 20% by atom, y is 20% or less by atom, and z is 0.001 to16% by atom), this permanent magnet having as the main phase thereof aphase having a ThMn₁₂-type structure. Additionally, Japanese PatentLaid-Open No. 4-241402 discloses that a rare earth-iron systemtetragonal compound having a stable ThMn₁₂-type structure can be formedby adding the element M (Si, Ti and the like); and Japanese PatentLaid-Open No. 4-241402 discloses that the element A (C, N) is effectivefor improving the Curie temperature.

Japanese Patent Laid-Open No. 5-65603 discloses an iron-rare earthsystem permanent magnet material comprising R: 3 to 30% by atom, X: 0.3to 50% by atom and the balance substantially composed of Fe where R isone element or a combination of two or more elements selected from thegroup consisting of Y, Th and all the lanthanoid elements, and X is oneof or a combination of the elements N (nitrogen), B (boron) and C(carbon), this permanent magnet material having as the main phasethereof a phase having a body-centered tetragonal structure. JapanesePatent Laid-Open No. 5-65603 further proposes that the magnet materialincludes M: 0.5 to 30% by atom by partially replacing Fe with theelement M (one element or a combination of two or more elements selectedfrom the group consisting of Ti, Cr, V, Zr, Nb, Al, Mo, Mn, Hf, Ta, W,Mg, Si, Sn, Ge and Ga). In Japanese Patent Laid-Open No. 5-65603, theelement M is regarded as an element having a significant effect ingenerating the body-centered tetragonal structure.

Additionally, Japanese Patent Laid-Open No. 2000-114017 discloses apermanent magnet material represented by a general formula(R_(1-u)M_(u)) (Fe_(1-v-w)Co_(v)T_(w))_(x)A_(y) (in this formula, R, M,T and A are respectively R: at least one element selected from rareearth elements inclusive of Y, M: at least one element selected from Tiand Nb, T: at least one element selected from Ni, Cu, Sn, V, Ta, Cr, Mo,W and Mn, A: at least one element selected from Si, Ge, Al and Ga; andu, v, w, x and y are respectively such that 0.1≦u≦0.7, 0≦v≦0.8, 0≦w≦0.1,5≦x≦12, and 0.1≦y≦1.5). This permanent magnet material has as the mainhard magnetic phase there of a ThMn₁₂-type structure. Japanese PatentLaid-Open No. 2000-114017 describes that substitution of the element Rwith the element M makes it possible to reduce the contents of Si, Geand the like which are the elements to stabilize the phase having theThM₁₂-type structure (hereinafter referred to as “ThM₁₂ phase” as thecase may be).

Rare earth permanent magnets are required to have high magneticproperties and on the other hand also to be low in cost. Among the rareearth elements constituting the rare earth permanent magnet, Nd is lowerin price than Sm, and hence it is preferable that Nd, inexpensivecompared to expensive Sm, makes the main component of the rare earthelements. However, the use of Nd makes the generation of the ThMn₁₂phase difficult, so that the production of the magnet concerned requiresa long time heat treatment at a high temperature. More specifically, forexample, annealing has been made at 900° C. for 7 days in the abovedescribed Japanese Patent Laid-Open No. 5-65603, and only Sm has beenused as the rare earth element except for some exceptions in JapanesePatent Laid-Open Nos. 4-241402 and 2000-114017.

In view of the above circumstances, the present invention takes as itsobject the provision of a hard magnetic compound capable of easilygenerating the ThMn₁₂ phase even when Nd is used as a rare earthelement, a permanent magnet powder and the like.

DISCLOSURE OF THE INVENTION

The present inventors have found that even when Nd is used as a rareearth element, a phase having a ThMn₁₂-type structure is easilygenerated by simultaneously adding predetermined amounts of Ti and Si.Additionally, it has also been found that sufficient magnetic propertiesas a hard magnetic compound for use in permanent magnets are obtained byfurther adding N and/or C to a compound obtained by simultaneouslyadding predetermined amounts of Ti and Si.

The present invention has been perfected on the basis of the abovefindings, and is a hard magnetic compound represented by a generalformula R (Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(Z)A_(v) (in the generalformula, R is at least one element selected from rare earth elements(here, the rare earth elements signify a concept inclusive of Y) and Ndaccounts for 50 mol % or more of R, and A is N and/or C), characterizedin that the molar ratios in the general formula are such that x=10 to12.5, y=(8.3−1.7×z) to 12.3, z=0.1 to 2.3, v=0.1 to 3, and w=0 to 30,and the relation (Fe+Co+Ti+Si)/R>12 is satisfied.

Additionally, the present inventors have found that by partiallyreplacing R with Zr and/or Hf, there can be obtained a hard magneticcompound which exhibits a higher saturation magnetization. In this case,the magnetic compound concerned is represented by a general formula,R1_(1-u)R2_(u)(Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(Z)A_(v) (in the generalformula, R1 is at least one element selected from rare earth elements(here, the rare earth elements signify a concept inclusive of Y), and 50mol % or more of R1 is Nd; R2 is Zr and/or Hf; and A is N and/or C), andthe composition of the hard magnetic compound may be set so that themolar ratios in the general formula is such that u=0.18 or less, y=4.5to 12.3, x=11 to 12.8, z=0.1 to 2.3, v=0.1 to 3, and w=0 to 30, and therelation (Fe+Co+Ti+Si)/(R1+R2)>12 is satisfied.

For the purpose of enjoying the advantageous effect of the improvementof the saturation magnetization, the content (u) of the R2 element (Zrand/or Hf) is preferably 0.04 to 0.06.

Even when R is partially substituted with Zr and/or Hf, the hardmagnetic compound can be made to be substantially composed of a singlephase of a hard magnetic phase, and the hard magnetic phase can be madeto be of a ThMn₁₂-type structure. It is to be noted that, in the presentspecification, the partial substitution of R with Zr and/or Hf will bereferred to as “Zr(Hf) substitution,” as the case may be.

Irrespective as to whether the Zr(Hf) substitution is effected or not,the hard magnetic compound of the present invention can acquire a singlephase consisting of a hard magnetic phase even when Nd accounts for 70mol % or more of R, and the single phase can be made to be a phasehaving a ThMn₁₂-type structure.

In the hard magnetic compound of the present invention, it is preferablethat A is N.

Additionally, irrespective as to whether the Zr(Hf) substitution iseffected or not, it is preferable that x is 11 to 12.5, z is 0.2 to 2.0,v is 0.5 to 2.5 and w is 10 to 25.

According to the present invention as described above, there can beobtained a hard magnetic compound comprising an R—Ti—Fe—Si-A compound oran R—Ti—Fe—Co—Si-A compound (in the general formula, R is at least oneelement selected from rare earth elements (here, the rare earth elementssignify a concept inclusive of Y) and Nd accounts for 80 mol % or moreof R, and A is N and/or C), showing a single phase consisting of a hardmagnetic phase, having a saturation magnetization (σs) of 120 emu/g ormore, and having an anisotropic magnetic field (H_(A)) of 30 kOe ormore. This hard magnetic compound is cost-advantageous since Nd accountsfor 80 mol % or more of the above R.

Here, the single phase can be made to be a phase having a ThMn₁₂-typestructure.

The hard magnetic compound of the present invention can also exhibitexcellent magnetic properties such that the anisotropic magnetic field(H_(A)) is 40 kOe or more, and the saturation magnetization (σs) is 130emu/g or more.

From a viewpoint of lowering the cost for producing a permanent magnet,it is desired that no high-temperature long-time heat treatment isrequired even when Nd is used. Accordingly, the present inventorsinvestigated an intermetallic compound comprising R (R is at least oneelement selected from rare earth elements (here, the rare earth elementssignify a concept inclusive of Y)) and T (the transition metal elementsindispensably including Fe and Ti) which has a composition that themolar ratio of R to T is in the vicinity of 1:12. Consequently, thepresent inventors have found that a high saturation magnetization and ahigh anisotropic magnetic field are obtained without applying ahigh-temperature long-time heat treatment when Si is present as aninterstitial element, and moreover, that both of the saturationmagnetization and the anisotropic magnetic field are further improvedwhen N is present as an interstitial element.

Additionally, in the above described course of the study, the presentinventors have verified that although Si and N are common in that theyare interstitial elements, they are different in the interstitial effectwhich affects the crystal lattice. As will be described later in detail,Si has an effect to shrink the crystal lattice, in particular, thea-axis of the crystal lattice, but on the contrary, N has an effect toisotropically expand the crystal lattice. Consequently, as compared tothe hitherto known axial ratio of the c-axis to the a-axis (hereinafterdenoted by “c/a”) of the crystal lattice of the ThMn₁₂-type compoundbased on ASTM (American Society For Testing and Materials), the c/avalue of a new intermetallic compound produced by the present inventorsare larger. Incidentally, the c/a value of the ThMn₁₂-type compoundbased on ASTM is 0.558.

The present invention based on the above described findings provides ahard magnetic compound formed of a single phase consisting of anintermetallic compound comprising R and T (R is one or more of the rareearth elements inclusive of Y, and T is the transition metal elementsindispensably including Fe and Ti) in a molar ratio of R to T in thevicinity of 1:12, the hard magnetic compound being characterized in thatSi and A (A is one or two of N and C) are located as interstitialelements at the interstitial sites in the crystal lattice of theintermetallic compound.

In the hard magnetic compound of the present invention, the molar ratioof R to T is preferably 1:10 to 1:12.5.

The ThMn₁₂-type structure as referred to in present invention means astructure which can be identified to be of the ThMn₁₂-type structure byX-ray diffraction. However, the structure concerned is different in thec/a value from the ThMn₁₂-type compound defined by ASTM. Morespecifically, the ratio between the lattice constant of the c-axis andthe lattice constant of the a-axis in the crystal lattice of saidintermetallic compound is represented by c1/a1, and the ratio betweenthe lattice constant of the c-axis and the lattice constant of thea-axis in the crystal lattice of the ThMn₁₂-type compound based on ASTM(American Society For Testing and Materials) is represented by c2/a2(c2/a2=0.558), the relation, c1/a1>c2/a2, holds. In this case, Sianisotropically shrinks the crystal lattice, and A isotropically expandsthe crystal lattice, so that the relation, c1/a1>c2/a2, can be obtained.

As permanent magnet powders used for bonded magnets and the like,SmCo-magent powder and NdFeB-magnet powder have hitherto been known.From the viewpoint of lowering the cost, it is preferable that Nd,inexpensive compared to expensive Sm, makes the main component of therare earth elements. For this reason, magnet powders comprising theNd₂Fe₁₄B₁ phase have been widely used. However, more inexpensive magnetpowders are demanded.

For the purpose of obtaining such magnet powders, the present inventorshave been made various investigations. Consequently, the presentinventors have found that by making fine the structure of the hardmagnetic compound of the present invention, the hard magnetic compoundcan exhibit a sufficient coercive force as a permanent magnet powder.More specifically, the permanent magnet powder of the present inventionis represented by a general formulaR(Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(z)A_(v) (in this general formula, Ris at least one element selected from rare earth elements (the rareearth elements signify a concept inclusive of Y), Nd accounts for 50 mol% or more of R, and A is N and/or C), the permanent magnet powder beingcharacterized by having a composition in which the molar ratios in thegeneral formula are such that x=10 to 12.8, y=(8.3−1.7×z) to 12.3, z=0.1to 2.3, v=0.1 to 3, w=0 to 30, and a relation, (Fe+Co+Ti+Si)/R>12, issatisfied, and by being composed of a population of particles having amean grain size of 200 nm or less.

In the permanent magnet powder of the present invention, it ispreferable that each of particles constituting the powder includes asthe main phase a phase having a ThMn₁₂-type structure, in particular, asingle phase consisting of a phase substantially having the ThMn₁₂-typestructure.

In the permanent magnet powder of the present invention, even when Ndaccounts for 70 mol % or more of R, it is possible to obtain a singlephase consisting of a phase substantially having the ThMn₁₂-typestructure. Accordingly, the permanent magnet powder concerned isadvantageous for lowering the cost.

The permanent magnet powder of the present invention is, as describedabove, characterized by having a nanostructure. Such a nanostructure iscreated by applying a predetermined heat treatment to an amorphous ornanocrystalline powder subjected to quenching and solidification. In amethod for producing the permanent magnet powder of the presentinvention, at the beginning, there is produced a powder subjected toquenching and solidification which has a composition represented by ageneral formula, R (Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(z) (in this generalformula, R is at least one element selected from rare earth elements(the rare earth elements signify a concept inclusive of Y), and Ndaccounts for 50 mol % or more of R), and the molar ratios in the generalformula are such that x=10 to 12.8, y=(8.3−1.7×z) to 12.3, z=0.1 to 2.3,and w=0 to 30, and the relation (Fe+Co+Ti+Si)/R>12 is satisfied. Then,the powder is subjected to a heat treatment in which the powder ismaintained in an inert atmosphere in a temperature range between 600 and850° C. for 0.5 to 120 hours. Thereafter, the powder subjected to theheat treatment is subjected to nitriding or carbiding.

In the method for producing the permanent magnet powder of the presentinvention, the powder subjected to quenching and solidification exhibitsany structure of an amorphous phase, a mixed phase composed of anamorphous phase and a crystalline phase and a crystalline phase. Ofthese phases, from a viewpoint of easily controlling the grain sizeafter the successive heat treatment, the mixed phase composed of anamorphous phase and a crystalline phase, in particular, a mixed phaseenriched in the crystalline phase is preferable.

In the method for producing the permanent magnet powder of the presentinvention, the method for quenching and solidification is notparticularly specified. However, it is preferable to apply the singlecasting roll method, since it is more productive, provides reproduciblya desired structure after quenching and solidification and has otheradvantages. When the single roll casting method is applied, the rollperipheral velocity is preferably set within a range between 10 and 100m/s. A powder subjected to quenching and solidification within thisrange can exhibit any structure of an amorphous phase, a mixed phasecomposed of an amorphous phase and a crystalline phase, and acrystalline phase, although some differences may occur, depending onother conditions such as the composition of a desired alloy, the holediameter of the nozzle for discharging a melt and the material qualityof the roll.

In the method for producing the permanent magnet powder of the presentinvention, the heat treatment applied to the powder subjected toquenching and solidification serves to crystallize the amorphous phaseor to regulate the grain size of the grains constituting the crystallinephase.

By using the permanent magnet powder obtained by the present invention,a bonded magnet can be produced. The bonded magnet includes a permanentmagnet powder and a resin for bonding the permanent magnet powder. Thecrystalline hard magnetic particles, constituting the permanent magnetpowder, each are represented by a general formula,R(Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(z)A_(v) (in the general formula, R isat least one element selected from rare earth elements (here, the rareearth elements signify a concept inclusive of Y) and Nd accounts for 50mol % or more of R, and A is N and/or C), the crystalline hard magneticparticles being characterized in that the molar ratios in the generalformula are such that x=10 to 12.8, y=(8.3−1.7×z) to 12.3, z=0.1 to 2.3,v=0.1 to 3, and w=0 to 30, and the relation (Fe+Co+Ti+Si)/R>12 issatisfied.

From the viewpoint of the magnetic properties, the mean grain size ofthe hard magnetic particles in the bonded magnet of the presentinvention is preferably 200 nm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relations between the lattice constants(a-axis and c-axis, and c-axis/a-axis) and the Si content (z) in thehard magnetic compounds having the compositionsNd(Ti_(8.2)Fe_(91.8))_(11.9)Si_(z) andNd(Ti_(8.2)Fe_(91.8))_(11.9)Si_(z)N_(1.5);

FIG. 2 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 1 (Experimental Example 1);

FIG. 3A is a graph showing the relation between the Si content and thesaturation magnetization (σs);

FIG. 3B is a graph showing the relation between the Si content and theanisotropic magnetic field (H_(A));

FIG. 4 is a chart showing the results of X-ray diffraction for SamplesNos. 4, 7 and 45;

FIG. 5 is a graph showing the thermomagnetic curves for Samples Nos. 4,7, 33 and 45;

FIG. 6 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 1 (Experimental Example 2);

FIG. 7A is a graph showing the relation between the (Fe+Ti) content andthe saturation magnetization (σs);

FIG. 7B is a graph showing the relation between the (Fe+Ti) content andthe anisotropic magnetic field (H_(A));

FIG. 8A is a graph showing the relation between the (Fe+Ti) content andthe saturation magnetization (σs);

FIG. 8B is a graph showing the relation between the (Fe+Ti) content andthe anisotropic magnetic field (H_(A));

FIG. 9 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 1 (Experimental Example 3);

FIG. 10A is a graph showing the relation between the Ti content and thesaturation magnetization (σs);

FIG. 10B is a graph showing the relation between the Ti content and theanisotropic magnetic field (H_(A));

FIG. 11A is a graph showing the relation between the Ti content and thesaturation magnetization (σs);

FIG. 11B is a graph showing the relation between the Ti content and theanisotropic magnetic field (H_(A));

FIG. 12A is a graph showing the relation between the Ti content and thesaturation magnetization (σs);

FIG. 12B is a graph showing the relation between the Ti content and theanisotropic magnetic field (H_(A));

FIG. 13 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 1 (Experimental Example 4);

FIG. 14A is a graph showing the relation between the N content and thesaturation magnetization (σs);

FIG. 14B is a graph showing the relation between the N content and theanisotropic magnetic field (H_(A));

FIG. 15 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 1 (Experimental Example 5);

FIG. 16 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 1 (Experimental Example 6);

FIG. 17 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 2 (Experimental Example 7);

FIG. 18 is a chart showing the results of X-ray diffraction for SamplesNos. 63, 91 and 105;

FIG. 19 is an enlarged chart for the vicinity of the diffraction anglewhere the peak of α-Fe generates;

FIG. 20 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 2 (Experimental Example 8);

FIG. 21 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 2 (Experimental Example 9);

FIG. 22 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 2 (Experimental Example 10);

FIG. 23 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 2 (Experimental Example 11);

FIG. 24 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 2 (Experimental Example 12);

FIG. 25 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 2 (Experimental Example 13);

FIG. 26 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 2 (Experimental Example 14);

FIG. 27 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 3 (Experimental Example 15);

FIG. 28 is a graph showing the thermomagnetic curves for the samplesobtained in Example 3;

FIG. 29 is a table showing the compositions, magnetic properties, andphases of the samples obtained in Example 3 (Experimental Example 16);

FIG. 30 is a chart showing the results of X-ray diffraction for flakessubsequent to quenching and solidification;

FIG. 31 is a chart showing the results of X-ray diffraction for samplessubsequent to heat treatment;

FIG. 32 is a figure showing a result of observation by TEM of thestructure of the flake obtained with a roll peripheral velocity (Vs) of25 m/s and then subjected to heat treatment;

FIG. 33 is a figure showing a result of observation by TEM of thestructure of the flake obtained with a roll peripheral velocity (Vs) of75 m/s and then subjected to heat treatment;

FIG. 34 is a table showing results of magnetic properties measured afternitriding for Example 4 (Experimental Example 17); and

FIG. 35 is a table showing results of magnetic properties measured afternitriding for Example 4 (Experimental Example 18).

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the examples inclusive of the best mode for the hard magneticcompound, the permanent magnet powder, the method for producing thepermanent magnet powder and the bonded magnet of the present inventionwill be described below.

First, reasons for quantitatively limiting individual elements in thepresent invention will be described below.

[R (Rare Earth Element or Elements)]

R is an element or a set of elements indispensable for obtaining a highmagnetic anisotropy. For the purpose of generating the ThMn₁₂ phase as ahard magnetic phase, it is advantageous to use Sm, but in the presentinvention, Nd is made to account for 50 mol % or more of R, for thepurpose of obtaining merits for cost. The present invention makes itpossible to easily generate the ThMn₁₂ phase even when Nd accounts for50 mol % or more of R.

It is to be noted that the present invention allows inclusion of rareearth elements other than Nd, in addition to Nd. When such inclusion isthe case, it is preferable to include, together with Nd, at least oneelement selected from Y, La, Ce, Pr and Sm. Of these listed elements, Pris particularly preferable because Pr exhibits almost the sameproperties as Nd and accordingly yields the same values as Nd for themagnetic properties.

According to the present invention, even when the proportion of Nd in Ris as high as 70 mol % or more, or 90 mol % or more, a structure havingas the main phase the ThMn₁₂ phase that is a hard magnetic phase can beobtained, and furthermore, a single phase consisting of the ThMn₁₂ phasecan be obtained. As will be shown in the examples to be described later,according to the present invention, even when R includes only Nd, thatis, Nd accounts for 100 mol % of R, a single phase consisting of theThMn₁₂ phase that is a hard magnetic phase can be obtained.

[Si]

When Si is added simultaneously with Ti to R(Nd) and Fe, Si contributesto the stabilization of the ThMn₁₂ phase as a hard magnetic phase. Inthis case, Si is situated at the interstitial sites in the ThMn₁₂ phaseand has an effect to shrink the crystal lattice. When the Si content ismade less than 0.1 (in molar ratio, both here and hereinafter), a phasehaving the Mn₂Th₁₇-type crystal structure (hereinafter referred to asMn₂Th₁₇ phase) tends to segregate, while when the Si content exceeds2.3, α-Fe tends to segregate. Accordingly, in the present invention, itis recommended that z representing the Si content be set in a rangebetween 0.1 and 2.3. The Si content (z) is preferably 0.2 to 2.0, andfurther preferably 0.2 to 1.0.

Additionally, as for Si in relation to Fe, Co, Ti and R, it ispreferable that Si is contained in such a way that the relation (molarratio of Fe+molar ratio of Co+molar ratio of Ti+molar ratio ofSi)/(molar ratio of R)>12 is satisfied; this point will be describedlater.

[Ti]

Ti contributes to generation of the ThMn₁₂ phase. More specifically, byreplacing Fe by a predetermined amount of Ti, the generation of theThMn₁₂ phase is made easy. In order to obtain this effect to asufficient extent, it is necessary to set the lower limit of the Ticontent (y) in relation to the Si content. In other words, as will beshown in the examples to be described later, when the Ti content (y) isless than (8.3−1.7×z (Si content)), α-Fe and the Mn₂Th₁₇ phasesegregate. On the other hand, the Ti content (y) exceeds 12.3, thedecrease of the saturation magnetization becomes remarkable.Accordingly, in the present invention, the Ti content (y) is set between(8.3−1.7×z (Si content)) and 12.3. The Ti content (y) is preferably(8.3−1.7×z (Si content)) to 12, more preferably (8.3−1.7×z (Si content))to 10, and further preferably (8.3−1.7×z (Si content)) to 9.

Additionally, when the sum (x) of the Fe content and the Ti content isless than 10, both the saturation magnetization and the anisotropicmagnetic field are small, while when the sum (x) exceeds 12.5, α-Fesegregates. Accordingly, the sum (x) of the Fe content and the Ticontent is set between 10 and 12.5. The sum (x) of the Fe content andthe Ti content is preferably 11 to 12.5.

[A (N (Nitrogen) and/or C (Carbon))]

A is an element effective in improving the magnetic properties in such away that A is situated at the interstitial sites in the ThMn₁₂ phase andthereby expands the lattice of the ThMn₁₂ phase. However, when the Acontent (v) exceeds 3.0, the segregation of α-Fe is observed, while theA content (v) is less than 0.1, no sufficient improvement effects of themagnetic properties can be obtained. Accordingly, the A content (v) isset between 0.1 and 3.0.

The A content (v) is preferably 0.3 to 2.5, and further preferably 1.0to 2.5.

[Fe, Fe—Co]

In the hard magnetic compound according to the present invention, Fesubstantially accounts for the part of the composition that does notinclude the above described elements. However, it is effective tosubstitute a part of Fe with Co. As will be described in the example tobe described later, addition of Co increases the saturationmagnetization (σ_(s)) and the anisotropic magnetic field (H_(A)).Addition of Co is carried out preferably with an addition amount of 30or less in terms of molar ratio, and more preferably with a rangebetween 5 and 20. The addition of Co is not indispensable.

[(Molar ratio of Fe+molar ratio of Co+molar ratio of Ti+molar ratio ofSi)/(molar ratio of R)>12]

The respective contents of Fe, Co, Ti and Si are as described above, butit is important to satisfy the condition that (Fe+Co+Ti+Si)/R>12 for thepurpose of making the hard magnetic compound of the present invention beof the single phase consisting of the ThMn₁₂ structure. As will be shownin the examples to be described later, the saturation magnetization islow when the above described condition is not satisfied.

[Zr, Hf]

In the above, the composition of the hard magnetic compound according tothe present invention has been described.

The hard magnetic compound of the present invention may further containZr and/or Hf. Inclusion of Zr and/or Hf is effective in improving themagnetic properties, in particular, the saturation magnetization.

R is partially substituted with Zr and/or Hf in the above describedgeneral formula. When u representing the substitution content of Zrand/or Hf exceeds 0.18, the saturation magnetization becomes lower thanwhen u is null. Accordingly, when R is partially substituted with Zrand/or Hf, u is set at 0.18 or less (exclusive of 0). The value of u ispreferably 0.01 to 0.15, and further preferably 0.04 to 0.06.

Here is shown the Ti content (y) in the case where the Zr(Hf)substitution is carried out.

When the Zr(Hf) substitution is carried out, the Ti content (y) is setbetween 4.5 and 12.3. In this case, the Ti content (y) is set preferablybetween 5 and 12, more preferably between 6 and 10, and furtherpreferably between 7 and 9. In this connection, the sum (x) of the Fecontent, the Co content and the Ti content is set between 11 and 12.8,and preferably between 11.5 and 12.5.

The hard magnetic compound according to the present invention can beobtained by the production methods well known in the art.

As for the interstitial element N, a material originally containing Nmay be used. However, it is preferable that after a compound containingelements other than N has been produced, N is made to interstitiallyenter into the compound by a treatment (nitriding) in a gas or liquidcontaining N. As the gas capable of making N interstitially enter intothe compound, there can be used N₂ gas, a (N₂+H₂) mixed gas, NH₃ gas,and a mixed gas composed of these gases. The temperature for thenitriding may be set between 200 and 1000° C., and preferably between350 and 700° C. The nitriding time may be selected appropriately to fallwithin a range between 0.2 and 200 hours.

As for the treatment (carbiding) for making C enter into the compound,the relevant description is the same as for the case of N. In otherwords, a material originally containing C may be used; and after acompound containing elements other than C has been produced, thecompound may be heat treated in a gas or liquid containing C.Alternatively, by heat treating the compound with a solid materialcontaining C, C may be made to interstitially enter into the compound.Examples of the gas capable of making C interstitially enter into thecompound include CH₄, and C₂H₆ and the like. As a solid materialcontaining C, carbon black may be used. In the carbiding using thesematerials, the treatment conditions may be appropriately set within atemperature range and a treatment time similar to those for thenitriding.

<Crystal Structure>

Next, the crystal structure of the hard magnetic compound according tothe present invention will be described below.

The hard magnetic compound of the present invention includes R (R is atleast one element selected from rare earth elements (here, the rareearth elements signify a concept inclusive of Y)) and T (the transitionmetal elements indispensably including Fe and Ti), and is constituted ofan intermetallic compound having a composition falling in the vicinityof an R to T molar ratio of 1:12. At the interstitial sites in thecrystal of the intermetallic compound, Si is situated as an interstitialelement. Additionally, N is also situated as an interstitial element inthis crystal lattice.

As described above, both Si and N are situated at the interstitial sitesin the crystal to improve the magnetic properties. It is to be notedthat Si shrinks the crystal lattice, while N expands the crystallattice, Si and N being different in effect in such a way. Now, thispoint will be mentioned below.

FIG. 1 is graphs showing the relations between the lattice constants(c-axis and a-axis, and c-axis/a-axis) and the Si content (z) in thehard magnetic compounds having the compositionsNd(Ti_(8.2)Fe_(91.8))_(11.9)Si_(z) andNd(Ti_(8.2)Fe_(91.8))_(11.9)Si_(z)N_(1.5). The hard magnetic compoundsshown in FIG. 1 are the compounds disclosed in the examples to bedescribed later.

In FIG. 1, no large variations of the lattice constants due to additionof Si are found for the c-axis. However, for the a-axis, it can be seenthat addition of Si remarkably reduces the lattice constant. In otherwords, Si has a feature such that Si is situated interstitially in thecrystal to anisotropically shrink the crystal lattice.

Next, in FIG. 1, it can be seen that addition of N enlarges the latticeconstants for both the c-axis and the a-axis. In other words, N issituated in the interstitial sites in the crystal and isotropicallyexpands the crystal lattice. As described above, by shrinking orexpanding the crystal lattice, the saturation magnetization, the Curietemperature and the anisotropic magnetic field are improved. As can alsobe seen from FIG. 1, the effect of anisotropically shrinking the crystallattice, due to Si, is not altered even by addition of N. Additionally,the presence of Si shrinks the crystal lattice, and coexistence of N andSi makes remarkable the effect of Si in improving the anisotropy andmakes easier the generation of a single phase.

In FIG. 1, the plots carrying the symbol “ASTM” refer to the latticeconstant of the c-axis, the lattice constant of the a-axis and thelattice constant of the c-axis/the lattice constant of the a-axis forthe ThMn₁₂-type compound described in ASTM. It can be seen that thelattice constants for a composition represented byNd(Ti_(8.2)Fe_(91.8))_(11.9)Si_(z) with z equal to zero coincide withthe lattice constants of the ThMn₁₂-type compound described in ASTM.

The presence of Si at the interstitial sites in a crystal can beverified as follows. An investigation based on the X-ray diffractionmethod of the composition represented byNd(Ti_(8.2)Fe_(91.8))_(11.9)Si_(z) described above with z equal to zero,namely, a compound containing no Si and a compound containing Si wascarried out to reveal that no variation of the fundamental shapes of theobtained diffraction peaks was found between these compounds. Moreover,no peaks of Si or no peaks of the compounds between the constituentelements of the above described compound and Si, and no peaks of α-Fewere identified. Furthermore, with increasing content of Si, the latticeconstant of the a-axis was continuously decreased. From these findings,it can be verified that Si is situated at the interstitial sites in thecrystal.

Additionally, in the present invention, N atoms are situated at theinterstitial sites in the crystal to expand both the c-axis and thea-axis with almost the same proportions. On the contrary, Si is situatedat the interstitial sites in the crystal to shrink only the a-axis, sothat it is inferred that Si is situated at some particular sites in thecrystal lattice. At present, such sites of Si cannot be identified, butthe X-ray diffraction pattern ascribable to the ThMn₁₂-type compound isshown, so that it is understood that Si is situated at some particularinterstitial sites in the crystal.

Although the hard magnetic compound of the present invention exhibitsthe lattice constants different from those of the ThMn₁₂-type compounddescribed in ASTM, the hard magnetic compound concerned exhibits, inX-ray diffraction, a diffraction pattern identifiable as that of theThMn₁₂-type compound. Consequently, the hard magnetic compound of thepresent invention is identified as a ThMn₁₂-type compound. In the hardmagnetic compound of the present invention, it is preferable that thehard magnetic phase is made to have a ThMn₁₂-type crystal structure. Inparticular, from the viewpoint of the magnetic properties, it ispreferable that the hard magnetic phase is made to be substantiallyconstituted of a single phase consisting of a ThMn₁₂-type crystalstructure.

In the above, the hard magnetic compound of the present invention hasbeen described. Although the hard magnetic compound is suitable as amaterial for magnets, the present inventors have found that the hardmagnetic compound concerned can exhibit a sufficient coercive force as apermanent magnet powder by making fine structure of the hard magneticcompound. Now, the permanent magnet powder and the production methodthereof according to the present invention will be described below indetail.

[Structure of the Permanent Magnet Powder]

First, the structure of the permanent magnet powder of the presentinvention will be described.

The permanent magnet powder of the present invention is so fine that themean grain size thereof is 200 nm or less, preferably 100 nm or less,and more preferably 80 nm or less. With such a nanostructure, thepresent invention can develop the coercive force required for apermanent magnet powder. The method for obtaining such a nanostructurein the present invention will be described later. The grain size is avalue derived as follows: a quenched alloy subjected to a heat treatmentwas observed by TEM to identify individual grains and the areas of theindividual grains were obtained by image processing, and then thediameter of a circle having the same area as that of each of the grainswas taken as the grain size of the grain concerned. The mean grain sizewas obtained by measuring the individual sizes of about 100 grains foreach sample and taking the mean value thereof.

The permanent magnet powder of the present invention having ananostructure is made to have the ThMn₁₂ phase as the main phase, andmore preferably to be a single phase consisting of the ThMn₁₂ phase. Thejudgment as to whether the single phase consisting of the ThMn₁₂ phaseis actualized or not is made according to the criteria shown in theexample to be described later.

[Method for Producing the Permanent Magnet Powder]

Next, a method for producing the permanent magnet powder of the presentinvention will be described below.

The permanent magnet powder of the present invention is characterized,as described above, by having a nanostructure, and several methods canbe applied for obtaining such a nanostructure. For example, there can becited a method using melt spinning, a method using mechanical grindingor mechanical alloying, and a method using HDDR(Hydrogenation-Decomposition-Desorption-Recombination). Now, theproduction method using melt spun will be described below.

The production method using melt spun includes three main steps, namely,a step for melt spinning, a step for heat treatment and a step fornitriding. Each of these steps will be described below sequentially.

<Step for Melt Spinning>

In the step for melt spinning, the melt is obtained by melting the rawmetals blended so as to have the above described composition, and thenthe melt is subjected to quenching and solidification. Specific examplesof the solidification method include the single roll casting method, thetwin roll casting method, the centrifugal quenching method and the gasatomizing method. Of these methods, it is preferable to use the singleroll casting method. In the single roll casting method, melted alloy isdischarged from a nozzle and is made to collide with the peripheralsurface of a cooling roll so as to be quenched, and thus a quenchedstrip-like or flake-like alloy is obtained. The single roll castingmethod is higher in mass productivity and more satisfactory inreproducibility of quenching conditions compared with other melt spun.

The quenched and solidified alloy exhibits any structure form of anamorphous single phase, a mixed phase composed of an amorphous phase anda crystalline phase, and a single phase composed of a crystalline phase,depending on the composition of the alloy, and the peripheral velocityof the cooling roll. The amorphous phase is nanocrystallized by the heattreatment to be carried out later. A basis for prediction is such thatwith increasing peripheral velocity of the cooling roll, the proportionof the amorphous phase is increased.

When the peripheral velocity of the cooling roll becomes faster, theobtained quenched alloy becomes thinner, so that a more uniform quenchedalloy can be obtained. It is most desirable for the present inventionthat the alloy, after quenching and solidification, has a desirablestructure, but it is not easy to realize. On the other hand, it isneedless to say possible to nanocrystallize a single phase consisting ofan amorphous phase by a heat treatment after the single phase concernedhas been obtained. However, there is a fear that abnormal grain growthmay be caused by precedently formed nuclei lead to generation of coarsegrains. Accordingly, a preferable mode for the present invention is suchthat there is obtained a solidified structure which is rich in ananocrystalline phase and the balance is constituted of an amorphousphase.

For that purpose, the peripheral velocity of the cooling roll is setusually between 10 and 100 m/s, preferably between 15 and 75 m/s, andfurther preferably between 25 and 75 m/s. When the peripheral velocityof the cooling roll is set to be less than 10 m/s, grains become coarseand the desired nanostructure can hardly be obtained, while when theperipheral velocity of the cooling roll exceeds 100 m/s, the closecontact between the melted alloy and the peripheral surface of thecooling roll is degraded to prevent effective heat transfertherebetween. The equipment cost is also thereby raised. It ispreferable that the step for melt spinning is conducted in anonoxidative atmosphere such as an atmosphere of Ar gas or N₂ gas.

<Step for Heat Treatment>

The quenched alloy obtained by the step for melt spinning issuccessively subjected to a heat treatment. The heat treatment generatesa nanocrystal having the grain size required in the present inventionwhen the quenched alloy shows a single phase composed of an amorphousphase. Additionally, when the quenched alloy shows a mixed phasecomposed of an amorphous phase and a crystalline phase, the heattreatment nanocrystallizes the amorphous phase, and additionally,controls the grains so as to have the grain size required in the presentinvention. Moreover, when the quenched alloy shows a single phaseconsisting of a crystalline phase, the heat treatment controls thegrains thereof so as to have the grain size required in the presentinvention. Accordingly, as long as the nanostructure required by thepermanent magnet powder of the present invention is not obtained as thestate of the quenched alloy, it is necessary to apply this heattreatment.

The treatment temperature in the heat treatment is 600 to 850° C.,preferably 650 to 800° C., and further preferably 670 to 750° C. Thetreatment time depends on the treatment temperature, and usually set atapproximately 0.5 to 120 hours. It is preferable that the heat treatmentis conducted in a nonoxidative atmosphere such as an atmosphere of Argas or He gas, or a vacuum.

<Step for Nitriding>

After the heat treatment, the quenched alloy is subjected to nitriding.As for N that is an interstitial element, a raw material originallycontaining N may be used, but it is preferable that after a compoundcontaining elements other than N has been produced, N is made tointerstitially enter by treatment (nitriding) in a gas containing N or aliquid containing N. As a gas capable of making N interstitially enter,there can be used N₂ gas, a (N₂+H₂) mixed gas, NH₃ gas and mixed gasesconsisting of these gases. It is preferable that the treatment isconducted with these gases as high-pressure gases for the purpose ofaccelerating the nitriding.

The temperature for the nitriding may be set between 200 and 450° C.,and preferably between 350 and 420° C., the nitriding time may beappropriately selected within a range between 0.2 and 200 hours. As forthe treatment (carbiding) for making C enter interstitially, theprocedures concerned are similar to those in the case of N, and a rawmaterial originally containing C may be used, and after a compoundcontaining elements other than C has been produced, the compound may beheat-treated in a gas or liquid containing C. Alternatively, thecompound may be heat-treated together with a solid material containingC, to allow C penetrate therein interstitially. Examples of a gascapable of making C interstitially enter include CH₄, C₂H₆ and the like.As a solid material containing C, carbon black may be used. In thecarbiding with these materials, within a temperature range and a rangeof treatment time, similar to those for nitriding, the conditions can beset appropriately.

The fundamental steps for obtaining the permanent magnet powder of thepresent invention are as described above, and the alloy obtained by meltspun may be milled before the step for heat treatment, before the stepfor nitriding, or after the step for nitriding. This is because thealloy obtained by melt spun usually does not meet the size required forthe permanent magnet powder for use in bonded magnets. The milling isconducted in an inert gas such as Ar and N₂.

No particular constraint is imposed on the mean particle size of thepermanent magnet powder; however, the particle size is preferably suchthat in a particular particle, sections largely different from eachother in crystallinity are found as scarcely as possible, and such thatthe particle size makes the powder usable as a permanent magnet powder.More specifically, when applied to bonded magnets, it is usuallypreferable that the mean particle size is 10 μm or more; however, forthe purpose of ensuring sufficient resistance to oxidation, the meanparticle size is set at preferably 30 μm or more, more preferably 50 μmor more, and furthermore preferably 70 μm or more. The mean particlesize of these orders permits making high density bonded magnets. On theother hand, the upper limit of the mean particle size is preferably 500μm, and more preferably 250 μm. It is to be noted that the mean particlesize as referred to here can be specified by the median diameter D50.D50 is a particle size at which the sum of the masses of the particlesreaches 50% of the total mass of the whole particles when the masses ofthe particles are summed starting from the smallest size particles,namely, the cumulative frequency in the particle size distributiongraph.

The permanent magnet powder obtained as described above can be appliedto bonded magnets. Bonded magnets are produced by bonding the particlesconstituting the permanent magnet powder with a binder. Bonded magnetsare classified into several types according to the production methodsthereof. Examples of the types include a compression bonded magnet basedon the press molding and an injection bonded magnet based on theinjection molding. As binders, various resins are preferably used, butwhen metal binders are used, metal bonded magnets are made. Noparticular constraint is imposed on the types of resin binders, and theresin binders may be appropriately selected from various thermosettingresins and various thermoplastic resins such as epoxy resin and nylon.No particular constraint is also imposed on the types of metal binders.Additionally, no particular constraints are imposed on the variousconditions including the content ratio of a binder to the permanentmagnet powder and the pressure in molding, and the conditions may beappropriately set in the typical ranges concerned. It is to be notedthat for the purpose of avoiding coarsening the grains, it is preferableto avoid such methods that necessitate high temperature heat treatment.

In the above, the examples in which nanostructure is obtained by use ofmelt spun has been described. However, the present invention is notlimited to this method. As another method, there can be cited a methodusing mechanical grinding. This method includes three main steps,namely, a mechanical grinding step, a heat treatment step and anitriding step. Descriptions on the heat treatment step and thenitriding step will be omitted because these steps are the same as thosein the above described method using melt spun.

Mechanical grinding can convert a material having a crystallinestructure to a material consisting of an amorphous phase by successivelyapplying mechanical impact to alloy particles milled to a predeterminedparticle size. The mechanical impact may be exerted by use ofapparatuses known as milling machines such as a ball mill, a shaker milland a vibration mill. By treating alloy particles with these millingmachines, the structure of the particles can be made amorphous.

Alloy particles may be produced by use of conventional methods. Forexample, after an ingot having a predetermined compound has beenprepared, alloy particles can be obtained by milling the ingot.Alternatively, a strip-like material or a thin flake-like material,obtained by melt spun, may be subjected to mechanical grinding. In thisconnection, needless to say, if the belt-like or flake-like material isamorphous originally, no such grinding is needed.

An alloy powder made amorphous by applying mechanical grinding aresuccessively subjected to the heat treatment step and the nitriding stepto be able to yield the permanent magnet powder of the presentinvention. Additionally, by use of the permanent magnet powder, thebonded magnet of the present invention can be obtained.

As a method for obtaining a nanostructure, there is cited heat treatment(HDDR: Hydrogenation-Decomposition-Desorption-Recombination) in which atarget material is maintained at a high temperature in an atmosphere ofhydrogen, and then hydrogen is removed. In the present invention, ananostructure can be obtained also by applying this HDDR treatment. Thepermanent magnet powder of the present invention can be obtained bysuccessively applying the heat treatment step and the nitriding step toa powder having been subjected to the HDDR treatment. Additionally, byuse of the permanent magnet powder, the bonded magnet of the presentinvention can be obtained.

EXAMPLES

Next, the present invention will be described below in more detail withreference to specific examples.

Example 1

The experimental results (experimental examples 1 to 6) supporting theabove described reasons for limiting the range of the composition willbe described as Example 1. As described above, although the hardmagnetic compound of the present invention exhibits the latticeconstants different from those of the ThMn₁₂-type compound described inASTM, the hard magnetic compound concerned exhibits a diffractionpattern in X-ray diffraction identifiable as that of the ThMn₁₂-typecompound.

Experimental Example 1

At the beginning, description will be made on the experimental results(Experimental Example 1) for the z value (Si content) dependences of thephase state and the magnetic properties.

High purity Nd, Fe, Ti and Si metals were used as raw materials, andeach sample was prepared by means of the arc melting method in an Aratmosphere in such a way that its alloy composition may be representedby Nd—(Ti_(8.3)Fe_(91.7))₁₂—Si_(z). Successively, the alloy was milledwith a stamp mill and passed through a sieve with opening of 38 μm, andthen subjected to a heat treatment (nitriding) in which the alloy wasmaintained at 430 to 520° C. for 100 hours in a nitrogen atmosphere.After the heat treatment, each of the samples was subjected to achemical composition analysis and an identification of the formedphases, and measurements of the saturation magnetization (σs) and theanisotropic magnetic field (H_(A)) The results obtained are shown inFIGS. 2 and 3.

The identification of the formed phases was carried out on the basis ofthe X-ray diffraction method and the measurement of the thermomagneticcurve. For the X-ray diffraction, a Cu tube was used and measurement wasmade with a power output of 15 kW, to verify whether the peaks of theThMn₁₂ phase and the peaks of the other phases were observed. However,because the peaks of the Mn₂Th₁₇ phase almost coincide with the peaks ofthe ThMn₁₂ phase, the verification was difficult only with the X-raydiffraction method. Accordingly, for the identification of the formedphases, the thermomagnetic curves were also used. The thermomagneticcurves were measured by applying a magnetic field of 2 kOe to verifywhether the Tc (Curie temperature) for each of the phases other than theThMn₁₂ phase was observed. It is to be noted that in the presentinvention, “a single phase consisting of the ThMn₁₂ phase” means that nopeaks other than those of the ThMn₁₂ phase are observed by the abovedescribed X-ray diffraction method, no Tc other than that of the ThMn₁₂phase was observed by the above described measurement of thethermomagnetic curves, and the remanent magnetization found in theregion above the Tc concerned is 0.05 or less; it does not matter ifundetectable amounts of unavoidable impurities, unreacted substances andthe like are contained. For example, in the arc melting, sometimes thethermal uniformity during dissolving was insufficient to yield traces ofresidual unreacted phases (for example, Nd, α-Fe and the like), andsometimes Cu and the like from the sample holder were contained asunavoidable impurities, but the unavoidable impurities were not takeninto consideration as long as these impurities were not detected by theX-ray diffraction and thermomagnetic curve measurements. Specificexamples for the identification of the formed phases will be describedon the basis of FIGS. 4 and 5.

FIG. 4 is a chart showing the results of X-ray diffraction for SamplesNos. 4 and 7 and Sample No. 45 to be described later. As shown in FIG.4, for Samples Nos. 4 and 45, only the peaks indicating the ThMn₁₂ phasewere observed. However, for Sample No. 7, a peak ascribable to α-Fe wasable to be identified. As described above, the peaks of the Mn₂Th₁₇phase overlapped with the peaks of the ThMn₁₂ phase, so that the formerwere unable to be discerned from the latter on the graph concerned.

FIG. 5 shows the thermomagnetic curves for Samples Nos. 4 and 7 andSamples Nos. 33 and 45 to be described later. The Tc of the ThMn₁₂ phasewas found in the vicinity of 400° C. As shown in FIG. 5, the Tc of theMn₂Th₁₇ phase (2-17 phase) was identified on the lower temperature sideof the Tc of the ThMn₁₂ phase (Sample No. 33). Here, when the Tc otherthan the Tc of the ThMn₁₂ phase was not identified, and the remanentmagnetization on the temperature side higher than this Tc was 0.05 orless, the sample was recognized to be of single phase. Morespecifically, in each of Samples Nos. 4 and 45, the Tc other than the Tcof the ThMn₁₂ phase was not identified, and the remanent magnetizationon the temperature side higher than this Tc was 0.05 or less, andconsequently, Samples Nos. 4 and 45 each were identified to be of thesingle phase consisting of the ThMn₁₂ phase. In Sample No. 7, the Tcother than the Tc of the ThMn₁₂ phase was not identified, but it wasidentified that α-Fe segregated in addition to the ThMn₁₂ phase on thebasis of the fact that the remanent magnetization exceeded 0.05 on thetemperature side higher than this Tc and FIG. 4. Moreover, in Sample No.33, the Tc of the Mn₂Th₁₇ phase was identified, and the remanentmagnetization on the temperature side higher than the Tc of the ThMn₁₂phase exceeded 0.05, and consequently, it was identified that theMn₂Th₁₇ phase and α-Fe segregated in addition to the ThMn₁₂ phase.

As described above, in the present invention, when no phase other thanthe ThMn₁₂ phase is identified both in FIG. 4 (X-ray diffraction) andFIG. 5 (thermomagnetic curve), the phase is defined to be the singlephase consisting of the ThMn₁₂ phase.

The saturation magnetization (σs) and the anisotropic magnetic field(H_(A)) were derived from the magnetization curves for the direction ofthe axis of easy magnetization and the magnetization curves for thedirection of the axis of hard magnetization measured by use of a VSM(Vibrating Sample Magnetometer) at a maximum applied magnetic field of20 kOe. For the convenience of the measurement, the maximummagnetization value found on the magnetization curve for the directionof the axis of easy magnetization was taken as the saturationmagnetization (σs). The anisotropic magnetic field (H_(A)) was definedas the magnetic field value for which the line tangent, at 10 kOe, tothe magnetization curve for the direction of the axis of hardmagnetization intersected the saturation magnetization (σs) value.

As shown in FIGS. 2 and 3, in Sample No. 6 having no added Si, theMn₂Th₁₇ phase (hereinafter referred to as the 2-17 phase) and α-Fe werepresent in addition to the ThMn₁₂ phase (hereinafter referred to as the1-12 phase), and the anisotropic magnetic field (H_(A)) was particularlylow. On the contrary, it was found that in each of Samples Nos. 1 to 5having added Si, the phase was of the single phase composed of the 1-12phase, and the 1-12 phase was stabilized. These compounds each showingthe single phase composed of the 1-12 phase can acquire a saturationmagnetization (σs) of 130 emu/g or more and an anisotropic magneticfield (H_(A)) of 50 kOe or more. However, in Sample No. 7 having a Sicontent of 2.5, α-Fe segregated and the properties were lowered. InSample No. 8 having a (Fe+Ti) content of less than 10 and a Si contentof 2.5, both of the saturation magnetization (σs) and the anisotropicmagnetic field (H_(A)) were remarkably decreased. If soft magnetic α-Feis present, the portion containing such α-Fe generates a reversemagnetic domain at a low magnetic field (demagnetizing field).Accordingly, the coercive force becomes small as a result of easilypromoting the inversion of the magnetic domains in the hard magneticphase component, and accordingly the presence of α-Fe is not desirablefor permanent magnets required to have coercive force.

Within the scope of Samples Nos. 1 to 5, the anisotropic magnetic field(H_(A)) tends to be increased with increasing Si content, whereas thesaturation magnetization (σs) tends to be increased with decreasing Sicontent.

Experimental Example 2

In the same manner as in Experimental Example 1, each sample wasprepared in such a way that the composition concerned may be representedby Nd—(Ti_(8.3)Fe_(91.7))_(x)—Si_(z)—N_(1.5). The samples obtained eachwere analyzed for chemical composition, identified for phases, andmeasured for saturation magnetization (σs) and anisotropic magneticfield (H_(A)). The composition, the magnetic properties and the phasesof each of the samples obtained in Experimental Example 2 are shown inFIG. 6. The results of measurement of the saturation magnetization (σs)and the anisotropic magnetic field (H_(A)) for the Samples Nos. 9 to 11and 17 to 20 are shown in FIGS. 7A and B, respectively. Similarly, theresults of the measurement of the saturation magnetization (σs) and theanisotropic magnetic field (H_(A)) for the Samples Nos. 12 to 16, 21 and22 are shown in FIGS. 8A and B, respectively. It is to be noted thatExperimental Example 2 is an experiment carried out for the purpose ofinvestigating the effects of the x (Fe content+Ti content) and (x+z) (Fecontent+Ti content+Si content) on the phases, the saturationmagnetization (σs) and the anisotropic magnetic field (H_(A)).

As shown in FIGS. 6 to 8, when x is less than 10 (Samples Nos. 17 and21), the saturation magnetization (σs) is less than 120 emu/g, and inSample No. 17 having such a low z (Si content) as 1.1, the anisotropicmagnetic field (H_(A)) is as low as about 30. On the contrary, when thex exceeds 12.5 (Samples Nos. 20 and 22), α-Fe comes to segregate. Evenwhen x falls within a range between 10 and 12.5, the saturationmagnetization (σs) is as low as less than 120 emu/g and the anisotropicmagnetic field (H_(A)) is also as low as about 30 kOe for the (x+z) of12 or less (Samples Nos. 18 and 19).

In a contrast to the above, when x falls within a range between 10 and12.5 and (x+z) exceeds 12 (Samples Nos. 9 to 16), there can be obtaineda single phase consisting of the 1-12 phase, and having such propertiesas a saturation magnetization (σs) of 120 emu/g or more and ananisotropic magnetic field (H_(A)) of 50 kOe or more.

Experimental Example 3

In the same manner as in Experimental Example 1, each sample wasprepared in such a way that its composition concerned may be representedby Nd—(Ti_(y)Fe_(100-y))—Si_(1.0)—N_(1.5),Nd—(Ti_(y)Fe_(100-y))—Si_(1.5)—N_(1.5), orNd—(Ti_(y)Fe_(100-y))—Si_(2.0)—N_(1.5). The samples were analyzed forchemical composition, identified for phases, and measured for saturationmagnetization (σs) and anisotropic magnetic field (H_(A)). Thecomposition, the magnetic properties and the phases of each of thesamples obtained in Experimental Example 3 are shown in FIG. 9. Theresults of measurement of the saturation magnetization (σs) and theanisotropic magnetic field (H_(A)) for the Samples Nos. 23 to 25 and 33to 35 are shown in FIGS. 10A and B, respectively. Similarly, the resultsof the measurement of the saturation magnetization (σs) and theanisotropic magnetic field (H_(A)) for the Samples Nos. 26 to 28, 36 and37 are shown in FIGS. 11A and 11B, respectively. Additionally, theresults of the measurement of the saturation magnetization (σs) and theanisotropic magnetic field (H_(A)) for the Samples Nos. 29 to 32 and 38are shown in FIGS. 12A and 12B, respectively.

It is to be noted that Experimental Example 3 is an experiment carriedout for the purpose of investigating the effects of the y (Ti content)on the phases, the saturation magnetization (σs) and the anisotropicmagnetic field (H_(A)).

As shown in FIGS. 9 to 12, in any one of the cases where z (Si content)is 1.0, 1.5 and 2.0, when y (Ti content) is less than (8.3−1.7×z), α-Feand moreover, the 2-17 phase segregate (Samples Nos. 33, 34, and 36 to38). On the other hand, when y (Ti content) exceeds 12.3 to be 12.5, thesaturation magnetization (σs) is decreased to be less than 120 emu/g(Sample No. 35).

On the contrary to the above, when y (Ti content) falls within a rangebetween (8.3−1.7×z) and 12.3, a single phase composed of the 1-12 phase,namely, a structure of a single phase composed of the hard magneticphase is obtained, and a saturation magnetization (σs) of 130 emu/g ormore and moreover 140 emu/g or more, and an anisotropic magnetic field(H_(A)) of 50 kOe or more and moreover 55 kOe or more can be obtained(Samples Nos. 23 to 32).

Experimental Example 4

In the same manner as in Experimental Example 1, each sample wasprepared in such a way that the composition concerned may be representedby Nd—(Ti_(8.3)Fe_(91.7))₁₂—Si_(2.0)—N_(v). The samples obtained eachwere analyzed for chemical composition, identified for phases, andmeasured for saturation magnetization (σs) and anisotropic magneticfield (H_(A)). The composition, the magnetic properties and the phaseseach of the samples obtained in Experimental Example 4 are shown in FIG.13. The results of measurement of the saturation magnetization (σs) andthe anisotropic magnetic field (H_(A)) for the Samples Nos. 39 to 44 areshown in FIGS. 14A and B, respectively.

It is to be noted that Experimental Example 4 is an experiment carriedout for the purpose of investigating the effects of the v (N content) onthe phases, the saturation magnetization (σs) and the anisotropicmagnetic field (H_(A)).

As shown in FIGS. 13 and 14, when v (N content) is null, both of thesaturation magnetization (σs) and the anisotropic magnetic field (H_(A))are low (Sample No. 43). On the other hand, when v (N content) exceeds 3to be 3.5, α-Fe segregates (Sample No. 44).

On the contrary to the above, when v (N content) falls within a rangebetween 0.1 and 3, a single phase composed of the 1-12 phase, namely, astructure of a single phase composed of the hard magnetic phase isobtained, and a saturation magnetization (σs) of 120 emu/g or more andan anisotropic magnetic field (H_(A)) of 30 kOe or more can be obtained(Samples Nos. 39 to 42). From the viewpoint of the saturationmagnetization (σs) and the anisotropic magnetic field (H_(A)), it ispreferable that v (N content) is set within a range between 0.5 and 2.7,and moreover, between 1.0 and 2.5.

Experimental Example 5

In the same manner as in Experimental Example 1, each of the samplesshown in FIG. 15 was prepared and subjected to the identification of theformed phase, and the measurements of the saturation magnetization (σs)and the anisotropic magnetic field (H_(A)). The results obtained areshown in FIG. 15.

It is to be noted that Experimental Example 5 is an experiment carriedout for the purpose of investigating the dependence on the w (Cocontent) in Nd—(Ti_(8.3)Fe_(91.7-w)Co_(w))₁₂—Si_(z)—N_(1.5).

As can be seen from FIG. 15, in any one of the case where z (Si content)is 0.25 and the case where z (Si content) is 1.0, the saturationmagnetization (σs) and the anisotropic magnetic field (H_(A)) areimproved by increasing w (Co content), and such improvement effectreaches a peak for w (Co content) of about 20. Accordingly, inconsideration of the fact that Co is expensive, w (Co content) ispreferably 30 or less, and is more preferably set within a range between10 and 25. Within this range of w (Co content), the structure is of thesingle phase composed of the 1-12 phase.

Experimental Example 6

High purity Nd, Fe, Ti and Si metals were used as raw materials, andeach sample was prepared by means of the arc melting method in an Aratmosphere in such a way that its alloy composition may be representedby Nd—(Ti_(8.3)Fe_(91.7-w)Co_(w))₁₂—Si_(z). Successively, each alloy wasmilled with a stamp mill and passed through a sieve with opening of 38μm, and thereafter mixed with a C powder having a mean particle size of1 μm or less, and then the mixture thus obtained was heat-treated so asto be maintained at 400 to 600° C. for 24 hours in an Ar atmosphere.After the heat treatment, each of the samples was subjected to achemical composition analysis and an identification of the formedphases, and measurements of the saturation magnetization (σs) and theanisotropic magnetic field (H_(A)) The results obtained are shown inFIG. 16.

As shown in FIG. 16, also by adding C in place of N, the single phaseconsisting of the 1-12 phase can be obtained, and additionally, asaturation magnetization (σs) of 120 emu/g or more and an anisotropicmagnetic field (H_(A)) of 30 kOe or more can be obtained. In this case,C plays the same role as N.

Additionally, even when 1 to 25% of Nd is substitute with Pr, the sameresults as obtained for the other samples can be obtained.

Example 2

The results of the experiments (Experimental Examples 7 to 14) carriedout for the purpose of investigating the variations of the magneticproperties caused by partial substitution of Nd with Zr or Hf will bedescribed below as Example 2. In Experimental Examples 7 to 13, Nd ispartially substituted with Zr, while in Experimental Example 14, Nd ispartially substituted with Hf.

Experimental Example 7

High purity Nd, Zr, Fe, Ti and Si metals were used as raw materials, andeach sample was prepared by means of the arc melting method in an Aratmosphere in such a way that its alloy composition may be representedby Nd_(1-x)Zr_(x)(Ti_(8.3)Fe_(91.7))₁₂Si_(1.0). Successively, accordingto the same procedures as in Example 1, each of the samples wassubjected to the milling and the heat treatment (nitriding). After theheat treatment, each of the samples was subjected to a chemicalcomposition analysis and an identification of the formed phases, and,under the same conditions as in Example 1, measurements of thesaturation magnetization (σs) and the anisotropic magnetic field (H_(A))were carried out. The results obtained are shown in FIG. 17.

As shown in FIG. 17, by partially replacing Nd by Zr, a saturationmagnetization (σs) of 140 emu/g or more can be obtained. The improvementeffect of the saturation magnetization (σs) provided by Zr exhibits apeak at a Zr content (u) of 0.05, and the Zr content exceeding thisvalue tends to decrease the saturation magnetization (σs); and when theZr content (u) comes to be 0.20, saturation magnetization (σs) becomeslower than when Zr is not contained. Additionally, when the Zr content(u) falls within a range between 0.02 and 0.15, the single phaseconsisting of the ThMn₁₂ phase (hereinafter referred to as the 1-12phase) is obtained.

From the above, the Zr content (u) is preferably set within a rangebetween 0.01 and 0.18, and more preferably within a range from 0.04 and0.06, on the basis of the general formulaR1_(1-u)R2_(u)(Ti_(y)Fe_(100-y-w)Co_(w))_(x)Si_(z)A_(v).

For each of the samples having been subjected to the heat treatment, theidentification of the formed phases was carried out by the X-raydiffraction method. The conditions of the X-ray diffraction were set tobe the same as in Example 1, and the presence or absence of the peaks ofthe ThMn₁₂ phase and the peaks of the phases other than the ThMn₁₂ phasewas investigated. As for the other phases, there can be cited α-Fe, theMn₂Th₁₇ phase and a nitride of Nd. For the purpose of obtaining highmagnetic properties, it is preferable that the main diffraction lines ofthe phases other than the ThMn₁₂ phase have peak intensity ratios of 50%or less in relation to the main diffraction line of the ThMn₁₂ phase.Specific examples of the identification of the formed phases will bedescribed below on the basis of FIGS. 18 and 19.

FIG. 18 is a chart showing the results of the X-ray diffractionmeasurement for Samples Nos. 63, 91 and 105 to be described later; inSamples Nos. 63 and 91, only the peaks exhibiting the ThMn₁₂ phase wereobserved. On the contrary, in Sample No. 105, the peak of α-Fe was ableto be verified. It is assumed that in Sample No. 105, the N content wasexcessive and the ThMn₁₂ phase was thereby decomposed and accordinglyα-Fe segregated. This can be seen from the fact that in Sample No. 105,the peaks of the ThMn₁₂ phase are decreased in intensity, while the peakof α-Fe grows.

FIG. 19 is an enlarged chart for the vicinity of the diffraction anglegenerating the α-Fe peak. In the vicinity of this angle, the peak of theThMn₁₂ phase and the peak of α-Fe are close to each other. In Sample No.63, only the peak of the ThMn₁₂ phase was observed. In Sample No. 91,two peaks, namely, the peak of the ThMn₁₂ phase and the peak of α-Fewere observed, but in a case where such a small amount of α-Fe isinvolved, the effect on the properties is small. On the other hand, inSample No. 105, almost only the peak of α-Fe was observed, and as can beseen from FIG. 18, the peak intensity ratio of the main diffraction lineof α-Fe to the main diffraction line of the ThMn₁₂ phase observed in thevicinity of 42° is 50% or more. When such a large amount of α-Fesegregates, the degradation of the properties becomes remarkable.

Experimental Example 8

In the same procedures as in Experimental Example 7, each sample wasprepared in such a way that the composition concerned may be representedby Nd_(0.95)Zr_(0.05)(Ti_(8.3)Fe_(91.7))₁₂Si_(u)N_(1.5). The samplesobtained each were analyzed for chemical composition, identified forphases, and measured for saturation magnetization (σs) and anisotropicmagnetic field (H_(A)). The results obtained are shown in FIG. 20.

It is to be noted that Experimental Example 8 is an experiment carriedout for the purpose of investigating the effects of Si content (z) onthe phases, the saturation magnetization (σs) and the anisotropicmagnetic field (H_(A))

In Sample No. 69 having no added Si, the Mn₂Th₁₇ phase (hereinafterreferred to as the 2-17 phase) and the α-Fe phase were present inaddition to the 1-12 phase, and the anisotropic magnetic field (H_(A))was particularly low. On the contrary, it was found that in each ofSamples Nos. 70 to 73 having added Si, the phase was of the single phasecomposed of the 1-12 phase, and the 1-12 phase was stabilized. Thesecompounds each showing the single phase composed of the 1-12 phase canacquire a saturation magnetization (σs) of 140 or 145 emu/g or more andan anisotropic magnetic field (H_(A)) of 50 or 55 kOe or more. However,in Sample No. 74 having a Si content of 2.5, α-Fe segregated in a largeramount and the properties were lowered. If soft magnetic α-Fe ispresent, the portion containing such α-Fe generates a reverse magneticdomain at a low magnetic field (demagnetizing field). Accordingly, thecoercive force becomes small as a result of easily promoting theinversion of the magnetic domains in the hard magnetic phase component,and accordingly the presence of α-Fe is not desirable for permanentmagnets required to have coercive force.

Within the scope of Samples Nos. 70 to 73, the anisotropic magneticfield (H_(A)) tends to be increased with increasing Si content, whereasthe saturation magnetization (σs) tends to be increased with decreasingSi content.

Experimental Example 9

In the same procedures as in Experimental Example 7, each sample wasprepared in such a way that the composition concerned may be representedby Nd_(0.95)Zr_(0.05)(Ti_(8.3)Fe_(91.7))_(x)Si_(0.5)N_(1.5),Nd_(0.95)Zr_(0.05)(Ti_(8.3)Fe_(91.7))_(x)Si_(1.0)N_(1.5), orNd_(0.95)Zr_(0.05)(Ti_(8.3)Fe_(91.7))_(x)Si_(1.5)N_(1.5). The samplesobtained each were analyzed for chemical composition, identified forphases, and measured for saturation magnetization (σs) and anisotropicmagnetic field (H_(A)). The results obtained are shown in FIG. 21.

It is to be noted that Experimental Example 9 is an experiment carriedout for the purpose of investigating the effects of the “Fe content+Cocontent+Ti content (x)” and the “Fe content+Co content+Ti content+Sicontent (x+z)” on the phases, the saturation magnetization (σs) and theanisotropic magnetic field (H_(A)).

As shown in FIG. 21, when the “Fe content+Co content+Ti content (x)” isless than 11 (Samples Nos. 81, 83, 84 and 86), the saturationmagnetization (σs) is less than 140 emu/g. On the contrary, when x is 13(Sample No. 85), α-Fe segregates in a larger amount and the propertiesare lowered. Additionally, even when x falls within a range between 11and 12.5, if (x+z), namely, (molar ratio of Fe+molar ratio Co+molarratio of Ti+molar ratio of Si)/(molar ratio of R1+molar ratio of R2) islower than 12 to be 11.6 (Sample No. 82), the saturation magnetization(σs) exhibits a value of 140 emu/g or more, but the anisotropic magneticfield (H_(A)) is at the highest 40 kOe or lower.

On the contrary to the above, each of Samples Nos. 75 to 80 in which xfalls within a range between 11 and 12.8 and (x+z) exceeds 12 has asaturation magnetization (σs) of 140 emu/g or more and an anisotropicmagnetic field (H_(A)) of 50 kOe or more.

Experimental Example 10

In the same procedures as in Experimental Example 7, each sample wasprepared in such a way that the composition concerned may be representedby Nd_(0.95)Zr_(0.05)(Ti_(y)Fe_(100-y))₁₂Si_(1.0)N_(1.5),Nd_(0.95)Zr_(0.05)(Ti_(y)Fe_(100-y))₁₂Si_(1.5)N_(1.5), orNd_(0.95)Zr_(0.05)(Ti_(y)Fe_(100-y))₁₂Si_(2.0)N_(1.5). The samplesobtained each were analyzed for chemical composition, identified forphases, and measured for saturation magnetization (σs) and anisotropicmagnetic field (H_(A)). The results obtained are shown in FIG. 22.

It is to be noted that Experimental Example 10 is an experiment carriedout for the purpose of investigating the effects of the Ti content (y)on the phases, the saturation magnetization (σs) and the anisotropicmagnetic field (H_(A)).

In any one of the case where the Si content (z) is 1.5 and the casewhere it is 2.0, when the Ti content (y) is less than 5.0, α-Fesegregates and moreover, the 2-17 phase segregates, and both of thesaturation magnetization (σs) and the anisotropic magnetic field (H_(A))still remain at low values (Samples Nos. 94 and 99). On the other hand,the Ti content (y) exceeds 12.3 to be 12.5, the saturation magnetization(σs) is decreased to be less than 130 emu/g (Sample No. 90).

On the contrary to the above, each of Samples Nos. 87 to 89, 91 to 93,and 95 to 98, in which the Ti content (y) falls within a range between 5and 12.3, takes a single phase composed of the 1-12 phase, namely, asingle phase consisting of a hard magnetic phase, and can acquire asaturation magnetization (σs) of 140 or 150 emu/g or more and ananisotropic magnetic field (H_(A)) of 50 or 55 kOe or more.

Experimental Example 11

In the same procedures as in Experimental Example 7, each sample wasprepared in such a way that the composition concerned may be representedby Nd_(0.95)Zr_(0.05)(Ti_(y)Fe_(100-y))₁₂Si_(1.0)N_(v). The samplesobtained each were analyzed for chemical composition, identified forphases, and measured for saturation magnetization (σs) and anisotropicmagnetic field (H_(A)). The results obtained are shown in FIG. 23.

It is to be noted that Experimental Example 11 is an experiment carriedout for the purpose of investigating the effects of the N content (v) onthe phases, the saturation magnetization (σs) and the anisotropicmagnetic field (H_(A)).

As shown in FIG. 23, when the N content (v) is zero, both of thesaturation magnetization (σs) and the anisotropic magnetic field (H_(A))are low (Sample No. 100).

On the contrary to the above, Samples Nos. 101 to 104 in which the Ncontent (v) falls within a range between 1 and 3 each shows a singlephase composed of the 1-12 phase, namely, a single phase consisting of ahard magnetic phase, and can acquire a saturation magnetization (σs) of140 emu/g or more and an anisotropic magnetic field (H_(A)) of 45 or 50kOe or more. From the viewpoint of the saturation magnetization (σs) andthe anisotropic magnetic field (H_(A)), it is preferable that the Ncontent (v) is set to fall within a range between 0.5 and 2.7, andmoreover, between 1.0 and 2.5.

Experimental Example 12

In the same procedures as in Experimental Example 7, each sample wasprepared in such a way that the composition concerned may be representedby Nd_(0.95)Zr_(0.05)(Ti_(8.3)Fe_(91.7-w)Co_(w))₁₂Si_(0.25)N_(1.5) orNd_(0.95)Zr_(0.05)(Ti_(8.3)Fe_(91.7-w)Co_(w))₁₂Si_(1.0)N_(1.5). Thesamples obtained each were identified for phases and measured forsaturation magnetization (σs) and anisotropic magnetic field (H_(A)).The results obtained are shown in FIG. 24.

It is to be noted that Experimental Example 12 is an experiment carriedout for the purpose of investigating the effects of the Co content (w)on the phases, the saturation magnetization (σs) and the anisotropicmagnetic field (H_(A)).

As can be seen from FIG. 24, in any one of the case where the Si content(z) is 0.25 and the case where it is 1.0, both of the saturationmagnetization (σs) and the anisotropic magnetic field (H_(A)) areimproved by increasing Co content (w) and such an improvement effectreaches a peak for the Co content (w) of about 20. Accordingly, inconsideration of the fact that Co is expensive, the Co content (w) ispreferably 30 or less, and more preferably set to fall within a rangebetween 10 and 25. Within this range of the Co content (w), thestructure is of the single phase composed of the 1-12 phase.

Experimental Example 13

High purity Nd, Zr, Fe, Ti and Si metals were used as raw materials, andeach sample was prepared by means of the arc melting method in an Aratmosphere in such a way that its alloy composition may be representedby Nd_(0.95)Zr_(0.05)(Ti_(8.3)Fe_(91.7-w)Co_(w))₁₂Si_(z). Successively,the alloy was milled with a stamp mill and passed through a sieve withopening of 38 μm, and thereafter mixed with a C powder having a meanparticle size of 1 μm or less, and then the mixture thus obtained washeat-treated so as to be maintained at 400 to 600° C. for 24 hours in anAr atmosphere. After the heat treatment, each of the samples wassubjected to a chemical composition analysis and an identification ofthe formed phases, and measurements of the saturation magnetization (σs)and the anisotropic magnetic field (H_(A)). The results obtained areshown in FIG. 25.

As shown in FIG. 25, also by adding C in place of N, the single phaseconsisting of the 1-12 phase can be obtained, and additionally, asaturation magnetization (σs) of 140 or 150 emu/g or more and ananisotropic magnetic field (H_(A)) of 40 kOe or more can be obtained. Inthis case, C plays the same role as N.

Experimental Example 14

The results of an experiment carried out for the purpose ofinvestigating the variations of the magnetic properties due to partialsubstitution of Nd with Hf will be described below as ExperimentalExample 14.

In the same procedures as in Experimental Example 7, each sample wasprepared in such a way that the composition concerned may be representedby Nd_(1-u)Hf_(u)(Ti_(8.3)Fe_(91.7))₁₂Si_(1.0)N_(1.5). The samplesobtained each were analyzed for chemical composition, identified forphases, and measured for saturation magnetization (σs) and anisotropicmagnetic field (H_(A)) The results obtained are shown in FIG. 26.

As can be seen from FIG. 26, Hf has a similar effect to Zr.

Example 3

The results of experiments (Experimental Examples 15 and 16) carried outfor the purpose of investigating the variations of the c/a caused byinclusion of Si will be described below as Example 3.

Experimental Example 15

High purity Nd, Fe, Ti and Si metals were used as raw materials, andeach sample was prepared by means of the arc melting method in an Aratmosphere in such a way that its alloy composition may be representedby Nd—(Ti_(8.2)Fe_(91.8))_(11.9)—Si_(z) orNd—(Ti_(8.3)Fe_(91.7))₁₂—Si_(z). Successively, the alloy was milled witha stamp mill and passed through a sieve with opening of 38 μm, andthereafter subjected to a heat treatment (nitriding) in which themixture was maintained at 430 to 520° C. for 100 hours in an nitrogenatmosphere. After the heat treatment, each of the samples was subjectedto a chemical composition analysis and an identification of the formedphases, and under the same conditions as in Example 1, measurements ofthe saturation magnetization (σs) and the anisotropic magnetic field(H_(A)). The results obtained are shown in FIG. 27.

The identification of the phases was carried out on the basis of theX-ray diffraction method and the measurement of the thermomagneticcurve, in the same manner as in Example 1.

As can be seen from FIG. 27, in Samples Nos. 121 to 126, each having alarger c/a value than the c/a value of 0.552 of Sample No. 129 having noadded Si, the magnetic properties, in particular, the anisotropicmagnetic field (H_(A)) is improved. However, also by referring to FIG.28, it can be seen that the anisotropic magnetic field (H_(A)) isimproved with decreasing lattice constant of the a-axis until thelattice constant concerned is decreased to fall in a predeterminedrange, whereas the saturation magnetization (σs) tends to be decreased.In Sample No. 131 rich in the Si content, α-Fe segregates and both ofthe saturation magnetization (σs) and the anisotropic magnetic field(H_(A)) are decreased. In Sample No. 130 with no added N, the saturationmagnetization (σs) is low. As compared to the levels of the saturationmagnetization (σs) and the anisotropic magnetic field (H_(A)) of SampleNo. 129 which contains N but not Si and those of Sample No. 130 whichcontains Si but not N, the saturation magnetization (σs) and theanisotropic magnetic field (H_(A)) of each of Samples Nos. 121 to 126,according to the present invention, exhibit high values exceedingexpected ranges, revealing that simultaneous inclusion of Si and Nremarkably improve the magnetic properties.

FIG. 28 shows the thermomagnetic curves for the compositions of SamplesNos. 127, 128 and 132 compiled in FIG. 27. For each of Samples Nos. 127and 128, the Tc is found in the vicinity of 430° C., but no other Tc canbe identified. Accordingly, Samples Nos. 127 and 128 each are taken tobe of a single phase consisting of the ThMn₁₂ phase. For Sample No. 132,the Tc for a first phase can be identified in the vicinity of 400° C.Additionally, at 450° C., Sample No. 132 holds a magnetizationcorresponding to 20% of the magnetization at room temperature. Thisindicates that Sample No. 132 has a magnetic phase having a Tc of 450°C. or more. With increasing measurement temperature, the magnetizationthereof comes to be lost in the vicinity of 770° C., and accordingly,the existence of a second phase can be identified. From these resultsand the results of the X-ray diffraction, this second phase can be takenas α-Fe.

Experimental Example 16

The compounds shown in FIG. 29 were obtained in the same manner as inExperimental Example 15. For each of these compounds, in the same manneras in Experimental Example 15, the measurements of the saturationmagnetization (σs) and the anisotropic magnetic field (H_(A)), and theidentification of the formed phases were carried out. The resultsobtained are shown in FIG. 29.

As shown in FIG. 29, Samples Nos. 133 to 137 each having an (Fe+Ti)content (x), namely, the ratio of (Fe+Ti) to R falling within a rangebetween 10 and 12.5 acquire high magnetic properties such as asaturation magnetization (σs) of 120 or 130 emu/g or more and ananisotropic magnetic field (H_(A)) of 55 kOe or more. Additionally, thecompounds based on Samples Nos. 133 to 137 each show a single phaseconsisting of the ThMn₁₂ phase. On the contrary, in Sample No. 138having a ratio of (Fe+Ti) to R of 12.7, the segregation of α-Fe has beenverified in addition to the segregation of a compound having the ThMn₁₂phase. Additionally, in Samples Nos. 133 to 137, with decreasing ratioof (Fe+Ti) to R, the single phase remains, but both of the saturationmagnetization (σs) and the anisotropic magnetic field (H_(A)) aredecreased. From this tendency, the ratio of (Fe+Ti) to R is preferablyset at 10 or more.

Example 4

Examples shown above (Examples 1 to 3) are all related to hard magneticcompounds. In Example 4, specific examples related to permanent magnetpowders will be presented.

Experimental Example 17

The raw materials weighed so as to give the composition shown below weremelted in an Ar atmosphere, and subjected to quenching andsolidification. The quenching and solidification conditions are asfollows.

The obtained alloy consisted of 20 μm thick flakes. These flakesheat-treated so as to be maintained at 800° C. in an Ar gas atmospherefor 2 hours.

Moreover, the heat treated flakes were milled with a stamp mill to asize capable of passing a sieve having opening of 75 μm, and the thusmilled powder was subjected to nitriding. The nitriding conditions aresuch that the treatment temperature is 400° C., treatment time is 64hours and the atmosphere is a flow of N₂ (at atmospheric pressure)

-   -   Composition: Nd₁Fe_(9.15)Co_(2.0)Ti_(0.85)Si_(0.2)    -   Single roll casting method (the material of the roll: Cu)    -   Nozzle hole diameter: φ1 mm    -   Pressure of gas jet: 0.5 kg/cm²    -   Temperature of melt: 1400° C.    -   Roll peripheral velocity (Vs): 15, 25, 50 and 75 m/s

For each of the quenched and solidified flakes (sample) and theheat-treated sample, the phases was observed by means of an XRD (X-RayDiffractometer). The results obtained are shown in FIGS. 30 and 31. FIG.30 shows the results observed for the quenched and solidified sample,while FIG. 31 shows the results observed for the heat-treated sample.

As shown in FIG. 30, the peaks of the ThMn₁₂ phase were observed in thesamples obtained with the roll peripheral velocities (Vs) of 15 and 25m/s, whereas the peaks of the ThMn₁₂ phase were not observed butdiffraction lines characteristic to amorphous phases were observed inthe samples obtained with the roll peripheral velocities (Vs) of 50 and75 m/s.

As shown in FIG. 31, it has been verified that after heat treatment, anyone of the above mentioned roll peripheral velocities results in theThMn₁₂ phase dominating the main phase.

FIG. 32 is an image showing the results of the TEM (TransmissionElectron Microscope) observation of the structure of the sample obtainedwith the peripheral velocity of a roll (Vs) of 25 m/s and subjected tothe heat treatment. FIG. 33 is an image showing the results of the TEMobservation of the structure of the sample obtained with the rollperipheral velocity (Vs) of 75 m/s and subjected to the heat treatment.

As shown in FIGS. 32 and 33, it has been able to be verified that afterthe heat treatment, extremely fine nanostructure is exhibited. Morespecifically, the structure found after heat treatment varies as followsdepending on the roll peripheral velocity (Vs): in the sample obtainedwith the roll peripheral velocity (Vs) of 25 m/s, many grains having agrain size of about 25 nm were observed, and the largest grain size isabout 50 nm; on the contrary, in the sample obtained with 75 m/s, alarge number of grains having a grain size of about 10 nm were observed,and the largest grain size is about 100 nm.

Next, the magnetic properties of the samples after quenching andsolidification, after heat treatment and after nitriding were measuredby using a VSM (applied magnetic field: 20 kOe). The results obtainedare shown in FIG. 34. The N contents of the samples after nitriding areas follows:

-   Roll peripheral velocity (Vs)=25 m/s: 2.93 wt %-   Roll peripheral velocity (Vs)=75 m/s: 2.79 wt %

As shown in FIG. 34, it has been verified that by applying nitridingafter heat treatment, both the coercive force (Hcj) and the remanentmagnetization (σr) are improved, and the sufficient properties as apermanent magnet are obtained. In FIG. 34, the measurement results ofthe magnetic properties of a powder obtained in Comparative Example tobe described below are also shown; both of the coercive force (Hcj) andthe remanent magnetization (σr) thereof still remain at lower values ascompared to Example.

Comparative Example: Raw materials were weighed so as to give the samecomposition (Nd₁Fe_(9.15)Co_(2.0)Ti_(0.85)Si_(0.2)) as in the presentexample, the mixture of the raw materials was melted by high frequencymelting, the obtained melt was cast into a water-cooled Cu mold toproduce an alloy (the thickness of the alloy: 10 mm). The alloy wasmilled with a stamp mill in the same manner as in Example, and themilled alloy was subjected to the same heat treatment and the samenitriding as in the present Example to yield a powder.

Next, an epoxy resin was mixed in a content of 3 wt % in the powdersubjected to the nitriding(the relevant roll peripheral velocity (Vs):50 m/s), and the mixture thus obtained was stirred and compacted by useof a die having a φ10 mm cylindrical cavity at a compacting pressure of6 ton/cm² to obtain a compact. The compact was subjected to a curingtreatment at 150° C. for 4 hours to yield a bonded magnet. The bondedmagnet was subjected to a measurement of magnetic properties with a B—Htracer (applied magnetic field: 25 kOe). The results obtained are asfollows:Br=6700 G, Hcj=7980 Oe, (BH)max=8.5 MGOe.

Experimental Example 18

Quenched and solidified alloys having the compositions shown in FIG. 35were produced, and then the alloys were subjected to the heat treatmentand the nitriding. The conditions for the quenching and solidification,heat treatment and nitriding are as follows. The magnetic properties ofthe alloys were measured after having been subjected to the nitriding,and the results obtained are shown in FIG. 35.

—Quenching and Solidification—

-   -   Single roll casting method (the material of the roll: Cu)    -   Nozzle hole diameter: φ1 mm    -   Pressure of gas jet: 0.5 kg/cm²    -   Melting temperature: 1400° C.    -   Roll peripheral velocity (Vs): 50 m/s        —Heat Treatment—

Retention at 800° C. for 2 hours in an Ar gas atmosphere

—Nitriding—

Retention at 400° C. for 64 hours in a flow of N₂ gas (at atmosphericpressure)

As shown in FIG. 35, it can be verified that the application of thenitriding after the heat treatment is effective for the purpose ofobtaining a permanent magnet powder provided with high magneticproperties.

INDUSTRIAL APPLICABILITY

According to the present invention, there can be provided a hardmagnetic compound in which even when Nd is used as a rare earth element,the ThMn₁₂ phase is easily generated. In particular, according to thepresent invention, even when the content of Nd is 100 mol %, there canbe obtained a hard magnetic compound which shows a single phaseconsisting of the ThMn₁₂ phase, namely, a hard magnetic phase.

Additionally, according to the present invention, there can be obtaineda hard magnetic compound showing a single phase in which both of thesaturation magnetization and the anisotropic magnetic field are high, byuse of an intermetallic compound in which Si which anisotropicallyshrinks the crystal lattice and N which isotropically expands thecrystal lattice are made to be included as interstitial elements, andthe ratio of T to R is made to fall in the vicinity of 12.

Moreover, according to the present invention, there can be provided apermanent magnet powder which can easily generate the ThMn₁₂ phase evenwhen Nd is used as a rare earth element, and a method for producing thepermanent magnet powder. Additionally, according to the presentinvention, there can be obtained a bonded magnet for which such apermanent magnet powder is used.

1. A hard magnetic compound, characterized in that: the hard magneticcompound is represented by a general formulaR(Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(z)A_(v) (in the general formula, R isat least one element selected from rare earth elements (here the rareearth elements signify a concept inclusive of Y), Nd accounts for 50 mol% or more of R, and A is N and/or C); and the molar ratios in saidgeneral formula are such that x=10 to 12.5, y=(8.3−1.7×z) to 12.3, z=0.1to 2.3, v=0.1 to 3 and w=0 to 30, and the relation (Fe+Co+Ti+Si)/R>12 issatisfied; wherein said hard magnetic compound shows a single phaseconsisting of a phase having a ThMn₁₂-type structure.
 2. The hardmagnetic compound according to claim 1, characterized in that Ndaccounts for 70 mol % or more of said R.
 3. The hard magnetic compoundaccording to claim 1, characterized in that said R is partiallysubstituted with Zr and/or Hf.
 4. A hard magnetic compound,characterized in that: the hard magnetic compound is represented by ageneral formula R1_(1-u)R2_(u)(Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(z)A_(v)(in the general formula, R1 isat least one element selected from rare earth elements (here, the rareearth elements signify a concept inclusive of Y), Nd accounts for 50 mol% or more of said R1, R2 is Zr and/or Hf and A is N and/or C); and themolar ratios in said general formula are such that u=0.18 or less, y=4.5to 12.3, x=11 to 12.8, z=0.1 to 2.3, v=0.1 to 3 and w=0 to 30, and therelation (Fe+Co+Ti+Si)/(R1+R2)>12 is satisfied; wherein said hardmagnetic compound shows a single phase consisting of a phase having aThMn₁₂-type structure.
 5. The hard magnetic compound according to claim4, characterized in that said u is 0.04 to 0.06.
 6. The hard magneticcompound according to claim 1 or 4, characterized in that said A is N.7. The hard magnetic compound according to claim 1 or 4, characterizedin that said x is 11 to 12.5.
 8. The hard magnetic compound according toclaim 1 or 4, characterized in that said z is 0.2 to 2.0.
 9. The hardmagnetic compound according to claim 1 or 4, characterized in that saidv is 0.5 to 2.5.
 10. The hard magnetic compound according to claim 1 or4, characterized in that said w is 10 to
 25. 11. A permanent magnetpowder, characterized in that: the composition of the permanent magnetpowder is represented by a general formulaR(Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(z)A_(v) (in the general formula, R isat least one element selected from rare earth elements (here the rareearth elements signify a concept inclusive of Y), Nd accounts for 50mol% or more of said R, and A is N and/or C); the molar ratios in saidgeneral formula are such that x=10 to 12.8, y=(8.3−1.7×z) to 12.3, z=0.1to 2.3, v=0.1 to 3 and w=0 to 30, and the relation (Fe+Co+Ti+Si)/R>12 issatisfied; the mean crystal grain size of the permanent magnet powderparticles is 200 nm or less; and said articles show a single phaseconsisting of a phase substantially having a ThMn₁₂-type structure. 12.The permanent magnet powder according to claim 11, characterized in thatNd accounts for 70 mol% or more of said R.
 13. A method for producing apermanent magnet powder, characterized by comprising the steps of:producing a powder by quenching and solidification of a melt of alloywherein: the composition of the powder is represented by a generalformula R(Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(z)(in the general formula, Ris at least one element selected from rare earth elements (here the rareearth elements signify a concept inclusive of Y), Nd accounts for 50mol% or more of said R); and the molar ratios in said general formulaare such that x=10 to 12.8, y=(8.3 −1.7×z) to 12.3, z=0.1 to 2.3 and w=0to 30, and the relation (Fe+Co+Ti+Si)/R>12 is satisfied; heat-treatingsaid powder so that the powder is maintained in an inert atmosphere at650 to 850° C. for 0.5 to 120 hours; and nitriding or carbiding saidheat-treated powder.
 14. The method for producing a permanent magnetpowder according to claim 13, characterized in that the structure ofsaid quenched and solidified powder is any one of an amorphous phase, amixed phase composed of an amorphous phase and a crystalline phase and acrystalline phase.
 15. The method for producing a permanent magnetpowder according to claim 13, characterized in that said quenching andsolidification is conducted by the single roll casting method, and theperipheral velocity of the roll in use is 10 to 100 m/s.
 16. The methodfor producing a permanent magnet powder according to claim 13,characterized in that said heat treatment crystallizes the amorphousphase, or regulates the size of grains constituting the crystallinephase.
 17. A bonded magnet comprising a permanent magnet powder and aresin phase to bind said permanent magnet powder, characterized in that:the composition of the crystalline hard magnetic particles constitutingsaid permanent magnet powder is represented by a general formulaR(Fe_(100-y-w)Co_(w)Ti_(y))_(x)Si_(z)A_(v) (in the general formula, R isat least one element selected from rare earth elements (here the rareearth elements signify a concept inclusive of Y), Nd accounts for 50mol% or more of said R, and A is N and/or C); the molar ratios in saidgeneral formula are such that x=10 to 12.8, y=(8.3 −1.7×z) to 12.3,z=0.1 to 2.3, v=0.1 and w=0 to 30, and the relation (Fe+Co+Ti+Si)/R>12is satisfied; and the articles of said permanent magnet powder show asingle phase consisting of a phase substantially having the ThMn₁₂-typestructure.
 18. The bonded magnet according to claim 17, characterized inthat the mean crystal grain size of said hard magnetic particles is 200nm or less.